1. Field of this Invention
This invention relates to a process for producing a 2,3-dihalopropionitrile which is a compound useful as a material for producing polymeric compounds or biologically active substances such as amino acids, agricultural chemicals and pharmaceuticals.
2. Prior Art
Conventional methods for producing 2,3-dihalopropionitriles by halogenation of acrylonitrile are carried out in various modes, for example, in the absence of a catalyst, or in the presence of a catalyst, or by utilizing a photo-radical reaction.
Various methods have been proposed for direct halogenation of acrylonitrile in the absence of a catalyst. For example, U.S. Pat. No. 2,231,360 and West German Patent No. 842,193 disclose a method for producing 2,3-dichloropropionitrile by introducing a chlorine gas into acrylonitrile in the presence of water. This method, however, is not commercially feasible because the yield of the product is as low as 26 to 29%. U.S. Pat. No. 2,298,739; C. Moureu and R. L. Brown, Bull. Soc. Chim. Fr., vol. 27, page 901, 1920; and L. Petit and P. Touratier, Bull. Soc. Chim. Fr., vol. 3, page 1136, 1968, disclose a method for producing 2,3-dihalopropionitriles by directly halogenating acrylonitrile with halogenating agents in chloroform or carbon tetrachloride as a solvent. This method, however, is not suitable for commercial practice because it requires recovery of the solvent. M. A. Naylor and A. W. Anderson, J. Am. Chem. Soc., vol. 75, page 5392, 1953; H. Brockmann and H. Musso, Chem. Ber., vol. 87, page 590, 1954; and U.S. Pat. No. 2,710,304 disclose a method for producing 2,3-dibromopropionitrile by the direct action of bromine on acrylonitrile. According to this method, the yield is as low as 70 to 89%. Elsewhere, A. V. Dombrovskii, Zhur. Obshch. Khim., vol. 24, page 610, 1954, discloses dibromination of acrylonitrile with dioxane dibromide as a halogenating agent. This method, however, is not commercially feasible because the use of the special halogenating agent adds to the cost of production and the yield of the product is as low as 50 to 55%.
Methods using catalysts have also been proposed. For example, H. Brintzinger, K. Pfannstiel and H. Koddebusch, Angew. Chem., vol. A(60), page 311, 1948; W. H. Jura and R. J. Gaul, J. Am. Chem. Soc., vol. 80, page 5402, 1958; S. S. Ivanov and M. M. Koton, Zhur, Obshch. Khim., vol. 28, page 139, 1958; and N. O. Pastushak, A. V. Dombrovskii and L. I. Pogovik, Zhur. Obshch. Khim., vol. 34 (7), page 2243, 1964, disclose halogenation of acrylonitrile in the presence of a pyridine catalyst. According to this method, the reaction mixture obtained by the reaction should be washed with water in order to remove the pyridine catalyst. Consequently, a part of the resultant 2,3-dihalopropionitrile dissolves in water together with the unreacted acrylonitrile to cause a decrease in the yield of the desired product. It also gives rise to a problem of treating the waste water. A method of halogenating acrylonitrile in the presence of an N,N-dimethyl formamide catalyst is disclosed in I. P. Losev, O. V. Smirnova and L. M. Lutsenko, Trudy Moskov. Khim. Tekhnol. Inst. im. D. I. Mendeleeva, vol. 29, page 17, 1959, and M. A. Askarov, K. A. Avlyanov and A. B. Alovitdinov, Uzbeksk. Khim. Zh., vol. 7(5), page 50, 1963. In this method, 2,3-dichloropropionitrile is obtained in a yield of 92.3% by adding 3% by weight of N,N-dimethyl formamide to acrylonitrile and chlorinating it. The inventors of the present application have traced this method and found that when the amount of N,N-dimethyl formamide is 3% by weight, the conversion of acrylonitrile is as low as 40 to 45%. Hence, this method is not commercially viable.
Production of a 2,3-dihalopropionitrile by photo-radical reaction is disclosed, for example, in W. W. Moyer Jr., T. Anyos and J. L. Dennis Jr., J. Org. Chem., vol. 31 (4), page 1094, 1966, and Dutch Laid-Open Patent No. 6,612,041. According to this technique, the 2,3-dihalopropionitrile is obtained from acrylonitrile by photo-radical reaction using an alkali metal hydrogen phosphate as an ionic reaction inhibitor. U.S. Pat. No. 2,390,470 and N. B. Lorette, J. Org. Chem., vol. 26, page 2324, 1961, disclose a method in which photochlorination of acrylonitrile is carried out in the absence of an additive. According to these methods involving photo-radical reaction, the yield of the 2,3-dihalopropionitrile is low, and the reaction apparatus becomes complex because photo-reaction is carried out therein. Hence, for commercial practice, these methods give rise to many problems.